U.S. Pat. No. 3,661,680 discloses a process for making an absorbent core comprising a layered construction of tissue, airfield and tissue. The process is indicated to combine the absorbent core by pressure rolls, however, by crimping along selected longitudinal lines. No cross-linked fibers and no super absorbent polymers are mentioned.
EP-A-593 relates to pad integrity improvements by use of a selected tissue which is placed between fibrous pads. Therefore this is the closest prior art for the basic core construction according to the present invention. However only compression to density but no crimping to join the fibrous pads to the tissue is mentioned.
EP-A-21662 relates to a wicking improvement by use of a special pattern of embossing a fibrous core to a tissue. However, no benefit for the core integrity is indicated and the process to make the absorbent core construction does not mention crimping but shows a patterned compression roll.
EP-A-214190 discloses the crimping of multiple layers of tissue to immobilize particles trapped between the layers. The basic principle of longitudinal crimping lines also is disclosed however no cross-linked fibrous patch is mentioned.
EP-A-214867 discloses fibrous structures with embossed wicking lines. This is not related to core integrity but to the placement of the structure within the product. No crimping of tissue to fibrous material is mentioned and no cross-linked fibers are disclosed.
EP-A-399564 discloses wicking improvements due to the selective density of webs of cross-linked cellulose. Densification by calendering is disclosed however no mention of tissue to pad crimping or core integrity improvements are discussed.
When making absorbent articles it is desirable to have discontinuous patches of absorbent patches disposed on continues bands of absorbent material, e.g. tissue. This is particularly true for the highly effective but expensive cross linked fibers now starting to be used more and more in the industry. In particular when using high speed machinery the discontinuous patches have to be joined to the continuous bands or else it would not be possible to transport them. This has typically been done by gluing the patches to the tissue.
However, the leading and trailing ends of a patch are problematic to be glued due to on off characteristics of the glue delivery and application equipment, it also may cause manufacturing efficiency losses due to glue contamination. Therefore patches were often only glued to the tissue in their center leaving the leading and trailing ends without attachment to the tissue. This however then easily leads to flying patches during production, even further reducing productivity. All these problems are even aggravated if the process of making absorbent cores includes a turning point where the band of already combined material is turned upside down, which has been found useful in obtaining particular products.
Therefore the problem underlying the present invention is to provide an absorbent core comprising a first absorbent structure, a tissue and a second fibrous absorbent structure which is shorter than the tissue in one direction and otherwise not extending beyond the periphery of the tissue. The tissue being joined to the second absorbent structure by crimping.
Preferably the crimping is done along one or several discrete lines. Even so not necessary for the present invention it is preferred if the interface between tissue and the second absorbent structure is free of adhesives.
An additional aspect of the present invention is a continuous process for the manufacture of absorbent cores according to the above description, comprising the steps of placing a continuous tissue on a conveyer belt; forming and depositing in discrete sequence a second fibrous absorbent structure on the continuous tissue; joining the tissue and the second fibrous absorbent structure to each other by crimping; forming the first absorbent structure as a continuous band and placing it onto the tissue on the opposite side from where said first fibrous structure is placed and finally severing the continuous band of tissue and first absorbent structure between one and the following of the second absorbent structures.